Vacuum tube



Dec. 5, 1933. w. VAN B. ROBERTS VACUUM TUBE Filed Sept. 28, 1928 Patented Dec. 5, 1933 stares UNITE vAcUUM TUBE Walter van Braam Roberts, Princetom-N. J., as-

signer to Radio Corporationof America, a cor poration of Delaware I Application September 28,1928

SerialNo'. 308,976v

4 Claims. (Cl. 250 -275) This invention relates to vacuum tubes and more particularly to a vacuum tube having a cathode energized by an alternating current.

Usually, when an alternating current is utilized to heat the filament comprising the cathode of an electron'discharge device or vacuum tube, due to the difference of alternating potential across the filament terminals an objectionable hum manifests itself in the loud speaker of a radio receiver when one or more vacuum tubes of the character described are utilized therein.

The object of this invention is to provide an electron discharge device having a cathode energized by an alternating current which shall not have this hum characteristic. This is done by providing a filament which, although it is energized by an alternating current presents an equipotential surface. n I

By providing a filamentary cathode closed upon itself and by causing an alternating heating current to flow therein by induction, I obtain a cathode which presents a substantially equi-potential surface, and which, when utilized in a radio receiver does not cause humming.

The accompanying drawing illustrates ways in which the invention may be carried out and utilized in practice,

Figs. 1 and 2 of the drawing being diagrammatically and partly in section, plan and eleva- 30 tion views respectively, of a cathode and heating and supporting means therefor built according to my invention;

Fig. 3 shows a manner in which auxiliary electrodes may be placed about the cathode, and

Fig. 4 shows a rectifier structure utilizing the features of the invention. 1

Referring to Figs. 1 and 2 the numeral 1 indicates, an electron emitting filamentary cathode of the direct or indirect heater or coated type closed upon itself and surrounded preferably by an evacuated toroid 3 concentric therewith. The toroid or ring shaped container 3 is preferably made of glass. Cathode 1 acts as a short-circuited secondary of a transformer, the other elements of which comprise an iron core 5 which may be made of laminated strips of iron, and a primary coil 7 to which is fed an alternating current. The alternating current fed to the coil 7 may be stepped up or down if desired by another 50 transformer (not shown), the latter transformer being supplied from any available source of al-' ternating current as, for example, a house ligh ing supply. 7

Spacers 9 may be provided for supporting filament 1. They may consist of circular discsof a r they according to this invention. I

the cathode and electrode structure removed from ill metal or of an insulating material such as mica having suitable holes 11 formed therein for supporting the filament. If made of metal, as they may be, they will tend to'act as shields between different electrode systems grouped about the so cathode, and also by their heat dissipating action will reduce emission from the'cathode at points between different electrode systems. A. common lead 13 should alsobeprovided for all external circuits to be used in connection with-6'5 cathode 1.

Fig. 3' indicates amanner in which various electrodes may be grouped about a cathode built This figure shows the heating apparatus. Numerals 15, 1'7, 19 and 21 indicate anodes, and numerals 15- 17, 19 and 21 indicate the respective leads thereto. .N-umerals 23, 25, 2'7 and 29 indicate. leads leading to control electrode structures or grids mounted it; within anodes 15, 17,19 and 21 respectively. The anodes may be supported within an'evacuated envelope 3 by any suitable means such as spacers 45 built along lines similar to spacers 9 except that they should have holes provided therein suf- 8'0 ficiently large to accommodate the anodes. The control electrodes may be similarly supported by spacers (not shown) within the anodes. v

The three electrode systems comprising, for example, anode 15, the control electrode 23'and the portion of cathode 1 within anode 15, may be utilized either for rectification, production of oscillations or for amplification of radio frequency.

or audio frequency currents, or any combination thereof. If desired one of the three. electrode 90.,

systems may be utilized as a detectorin combination with the other three electrode systems. While I have illustrated astructure inwhich the filament cooperates with four grid plate structures, it is to be understood, of course, that any 95. l I

number of electrode. systems for. any purposes desired may be placed about filamentary cathode 1. A single lead-in 13 is shown in Fig.3 for making contact with the cathode but a greater number may be provided if desired. I

'As only filament 1 completely links with the magnetic circuit set up by the primary '7 of the transformer, currents will only be set up in the cathode 1, and no currents of any harmful valve will be set upiin the other electrodes of the device. Further, since cathode 1 is electrically closed upon itself and heavy currents of low potential are therefor generated therein by induction, between any two points thereof there cannot exist a substantial difference in potential duction.

7 envelope.

Fig. 4 diagrammatically shows an arrangement of anodes about a cathode built according to the invention for use as a full wave rectifier; Numerals indicate anodes, 41' theleads thereto, 42 the cathode and 42' the lead thereto. The cathode energizing system (not shown) is similar to that illustrated in Figs. 1 and 2.

t Although there has been shown forms in which my. invention may be carried out and utilized it to be understood that the scope of my invention is not to be limited thereby except as indicated in the appended claimsr a I I claim as my invention: V

1. An electron discharge device comprising a toroidal shaped evacuated envelope, a ring shaped cathode concentrically arranged therein, a plurality of partitions within and dividing the envelope into a pluralityof independent chambers, said partitions also acting to support the cathode at intermediate points thereof, grid and anode electrodes supported within each of the chambers and concentrically arranged about that portion of the cathode housed within the chamber, and means for heating the cathode by magnetic in- 2. An electron discharge device comprising an evacuated envelopa a. closed conductive circuit constituting a cathode mounted within the envelope, a magnetic circuit interlinked with'said cathode and substantiallysymmetrically disposed with respect thereto, a plurality of partitions within and dividing the envelope into a plurality of independent chambers, said partitions also acting to support the cathode at intermediate points thereof, and grid and anode electrodes supported within each of the chambers and concentrically arranged about that portion of the cathode housed Within the chamber.

3. An electron discharge device comprising a cathode and a plurality of cooperating electrodes arranged in groups along .said cathode, said cathode consisting of a closed metallic circuit substantially symmetrically disposed about an interlinking magnetic circuit which is also linked by a primary winding adapted to be connected to a source of alternating voltage, whereby said cathode is heated by induction without the development of'substantial differences of potential between any of its parts at any instant, and metallic shielding means interposed between said groups of cooperating electrodes to prevent the transfer of energy therebetween, said cooperating electrodes and shielding means. being connected to a source of alternating voltage, whereby said cathode is heated by inductionwithout thedevelopment of substantial differences-of potential between any of its parts at any instant, a plurality of groups of cooperating grid and plate electrodes disposed along diiierent sections of the cathode, and metallic shields interposed between adjacent electrode groups,

WALTER VAN RAAM RO E TS,

Ill)" its also linked by a primary winding adapted to be V 

